DITA supports many different linking elements,
but they all use the same set of attributes to describe
relationships between content.
URI-based links are described by the following attributes.
- The href attribute specifies the URI of the resource that is being
- The format attribute identifies the format of the resource being
addressed. For example, references to DITA topics are identified with
format="dita", whereas references to DITA maps use
format="ditamap". References to other types of content should use
other values for this attribute. By default, references to non-XML content use the
extension of the URI in the href attribute as the effective
- The scope attribute describes the closeness of the relationship
between the current document and the target resource. Resources in the same information
unit are considered "local"; resources in the same system as the
referencing content but not part of the same information unit are considered
"peer"; and resources outside the system, such as Web pages, are
- The type attribute is used on cross-references to describe the target
of the reference. Most commonly, the type attribute names the element
type being referenced when format="dita".
These four attributes act as a unit, describing whatever link is established by the element
that carries them.
The format and scope attributes are assigned default
values based on the URI that is specified in the href attribute. Thus they
rarely need to be explicitly specified in most cases. However, they can be useful in many
non-traditional linking scenarios or environments.
Indirect key-based addressing
DITA also supports indirect links and cross-references in which a DITA map assigns unique
names, or keys, to the resources being referenced by the publication. This is done using
topicref elements that specify the keys
attribute. Using the keyref attribute, individual links, cross-references,
and images then reference resources by their keys instead of their URIs . Links defined
using keyref thus allow context-specific linking behavior. That is, the
links in a topic or map might resolve to one set of resources in one context, and a
completely different set of resources in another, without the need for any modifications to
the link markup.
When links are defined using keyref, values for the four linking
attributes described above are typically all specified (or given default values) on the key